As long as the rod does not have a trigger reel seat you can do it, although most guys prefer a slightly longer butt section on a spinning rod ... Put a spinning reel on and see how you like the action (even with the existing small guides).
If you think the butt length is OK for you, then all you have to do is change the guides. Use a size 40 guide (Fuji or Pac Bay) as your stripping guide nearest the butt. This is not too big - I used a size 40 on a 8' surf spinning rod and it works great - only looks "funny" to the uninitiated!
After the size 40 stripping (butt guide) work your way up the rod with progressively smaller guides to the tip. If you are going to use braid or Fireline with a mono or fluoro leader do
not go smaller than size 12 guides on the tip and for the 3 guides nearest the tip (to accommodate the leader knot and to save you countless hassles ...). If you are not ever going to use a leader, you can get away with size 10 guides (last 3 nearest tip and tip).
Also do not use too few guides ...
This is a
general recommendation of eyes needed for a 10' surf spinning rod:
Butt40 30 25 20 16 16 12 12 12 12TIP
If the rod is longer, you may have to add one or two more 16's ...
It is a good idea to tape the guides to the blank first to check out
exactly how many guides you will need for your rod and how to space them properly when the blank is under load ... There must be no sharp angles of line anywhere when the rod flexes. Don't just assume you can put the spinning guides exactly where the original guides were on the rod. The butt or stripping guide on a rod built for a spinning reel is generally also placed a bit further from the face of the reel. There are no exact formulas for spacing guides - nothing takes the place of practical testing and flexing the rod with the guides taped in place using the reel and line you will ultimately use. Also try a few casts until you are happy
before finally fitting the guides permanently.
Hope this helps ... and enjoy the project!